Characterization of Building Envelopes and the Monitoring of Laser Power Using the gSKIN® Sensor

Dr. Susanne Dröscher, Sales Engineer at greenTEG talks to AZoSensors about characterization of building envelopes and the monitoring of laser power using the gSKIN^® sensor.

One of your most innovative products includes the gSKIN^® Heat Flux Sensor. How has the idea of human skin anatomy and physiology influenced the development of this product?

We all experience the phenomenon of heat flux in our everyday life. An example for this is the metallic surface of the door handle that feels colder than the wooden surface of the door frame – although they have the same temperature. Instead of actually exhibiting a lower temperature, the metallic door handle has a much larger heat capacity than the wooden frame and therefore withdraws more heat from the human body. With our skin we perceive this as a locally lowered temperature. Hence, the human skin can be seen as a heat flux sensor that provides qualitative information.

The gSKIN^® Heat Flux Sensor features this very property of the skin. However, it gives a quantitative analysis of the heat flux and is therefore useful in all applications where information about the dynamics of a thermal system is required. The sensor detects heat flux in the form of conduction, radiation as well as convection.

How does the gSKIN^® sensor work?

The gSKIN^® sensor is based on a phenomenon known from the field of thermo-electrics - called the Seebeck effect. It is widely-used in thermocouples applied as temperature sensors. When two electric conductors are joined and this junction is warmer than the open ends of the conductors, an electric voltage is built up. This voltage can be probed and related to the temperature difference between the junction and the open ends.

In the gSKIN^® sensor, many of these thermocouples are connected in series. The junctions are located on the upper side and on the lower side of the sensor alternately. A temperature difference across the sensor hence leads to a voltage bias. This output voltage is proportional to the temperature difference between the two sides and - since the thermal resistance of the sensor is constant - to the heat flux through the sensor.

Measurement of heat flux using the gSKIN sensor. Video courtesy of greenTEG.

What are the main applications for this sensor?

The gSKIN^® Heat Flux Sensor is used in the field of building physics e.g. to characterize building envelopes. For this purpose the sensors are embedded in the plaster at representative spots to monitor the heat flow in and out of the building. Moreover, the gSKIN^® is applied as a sensing element in building automation at various spots in a building.

As mentioned earlier, electromagnetic radiation can be measured with the gSKIN^® sensor as well. This property is employed e.g. for the control of laser systems, where the gSKIN^® Radiation Sensor provides the exact value of the optical power generated by the laser.

Are there any examples of application of the gSKIN^® sensor in building physics?

Materials used in building technology are examined extensively during their development in research labs. Properties like the heat conductivity and the K-value are so to speak the fingerprint of any new material. These parameters can be determined using the gSKIN^® sensor.

In a finished building it is important to understand the thermal transfer characteristics of its components. With a heat flux analysis, different rooms can be examined and compared. Furthermore, it is possible to quantify seasonal changes of heat transfer to understand the energy balance of a house.

Buildings become more and more automated. In self-actuating shading systems for windows, the information of the gSKIN^® Radiation Sensor is used to lower or raise the blinds.

How does the application of this sensor in building technology impact materials and construction methods and how does this affect energy consumption?

A very interesting example of lately developed building materials are phase changes materials (PCMs), which are e.g. integrated into walls. Due to a phase transition at a certain temperature they act as an absorber or provider for thermal energy, which improves the indoor climate without active heating or cooling. The conversion efficiency and heat storage capabilities of such a material is accurately evaluated with the gSKIN^® sensor by observing the heat flow as a function of time.

Another example for energy efficiency by building automation is an intelligent heating system. Instead of controlling the room climate by monitoring temperature, the actual heat transfer into or out of a room provides a more direct feedback on the necessary heating or cooling power.

What are the main benefits of the gSKIN^® sensor used in laser systems?

To ensure the trouble-free and uniform operation of a laser system and the safety of all staff handling it, the laser needs to be monitored carefully. A power sensor integrated into the laser system gives continuous feedback on the beam properties. Hence, scrap production can be lowered and high quality results are obtained.

The advantages of the gSKIN^® Radiation Sensor for this application are its fast response as well as its small dimensions and its mechanical robustness. This enables the easy integration into laser systems. Further, lasers of any wavelength can be measured with high accuracy. This is beneficial especially for infrared radiation where other technologies are limited.

Ultrafast lasers are getting popular in manufacturing and medical applications due to their low effect on material properties and tissue. Pulses in the pico and femtosecond range cannot be resolved by any current technology. Hence, the average power is the parameter of interest for theses lasers. Whereas semiconductor sensors are not suitable for average power measurements in such a system, the gSKIN^® Radiation Sensor (being a thermopile sensor) yields accurate values.  

You mentioned earlier that the gSKIN^® sensor provides detailed information about thermal systems in general. Do researchers use the sensor as a tool already?

The heat flux as a physical quantity provides a new perspective on established experiments. This yields a deeper understanding of a system and reveals valuable insights. Therefore, the gSKIN^® sensor is popular among researchers in various fields.

In the lab, easy handling of a measurement apparatus is a requirement. The sensing part as well as the read-out unit needs to be robust. Together with a partner, we have developed a data logger adjusted to the specifications of the gSKIN^® sensor. With the gSKIN^® sensor combined with a read-out system, measurements are set up within very short time and data recording is straightforward. Both live read-out and data storage is possible with this product.

I will mention two types of measurements carried out with gSKIN^® sensors:

To carry out a calorimetric characterization of a chemical reaction, the sensor is attached to the chemical reactor. During the reaction, heat energy is either released or absorbed, which causes a heat exchange between the inside and the outside of the reactor. From the measured amount of heat transferred through the container, the reaction energy is obtained.

For a solar radiation measurement, the gSKIN^® Radiation Sensor is mounted onto the surface of interest. The incident power can be read-out directly. In the field of e.g. meteorology and building physics, solar radiation sensors are an important data acquisition tool.

Are any development efforts in place to help advance this sensor technology to diversify its application?

Different applications require different sensor specifications and we have been inspired by our customer’s needs to introduce new products. One of the parameters to vary is the size of the sensor. A miniature sensor with an area of 4x4 mm² will be launched at the beginning of next year as the smallest heat flux sensor on the market. With this product we offer an economic solution for all applications where the size of the sensor matters.

Furthermore, the read-out unit is constantly developed to facilitate the integration of the sensors into established systems. Especially for our OEM customers, the interface between the sensor and the read-out electronics is an important topic. In the past, the low voltage level of the sensor output put limitations to some applications. We, therefore, engineered amplification electronics to obtain a signal range of 0-5V, which can be resolved by standard volt meters.

To reach out to a broad spectrum of retail customers, we will shortly open a web shop, where one can conveniently order the gSKIN^® sensors, read-out systems and many other products related to heat flux and radiation measurement.

How do you see the end-user market changing with the adaptation of this technology over the next 5 years?

The concept of heat flux measurements is new in many fields and is in general not simple to grasp. However, it adds valuable information to many systems and gives new possibilities for analysing and improving them. Since we launched the gSKIN^® sensor beginning of this year, a large number of applications has been revealed. Our task is to sensitize the different branches of industry to the opportunities the gSKIN^® sensor provides.

Combining the sensor with intelligent control units has the potential to, for example, run production processes more uniformly, monitor medical patients more reliably, manage buildings more energy efficiently and detect fouling in pipes earlier.

Where can we find further information on your products and services?

We have produced several videos that introduce the physical quantity heat flux by means of every day examples and show possible applications for the gSKIN^® sensor. All videos are published on our YouTube channel.

On our website, product information is available. For various applications we have compiled Application Notes, which describe in detail the use of the gSKIN^® sensor in different scenarios.

For more specific questions, our team can be contacted directly as well.

About Dr. Susanne Dröscher

Susanne has a background in material’s science and physics. She received her PhD from ETH Zurich in 2012 and afterwards joined the greenTEG AG as a Sales Engineer.

At greenTEG she works on the development and customization of products, which are adapted to the user’s requirements. These projects are carried out with close contact to the customers involving technical discussions and consulting.